, Volume 58, Issue 5, pp 513-518

Femtosecond-pulse laser ablation of human corneas

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Abstract

A femtosecond pulse laser in the visible spectral region shows promise as a potentially new powerful corneal sculpting tool. It combines the clinical and technical advantages of visible wavelengths with the high ablation quality observed with nanosecond-pulse excimer lasers at 193 nm. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs and 7 ns, and centre wavelengths at 615 nm and 600 nm, respectively, both focused to an area of the order of 10−5 cm2, have been applied to human corneal ablation. Nanosecond laser pulses caused substantial tissue disruption within a 30–100 μm range from the excision edge at all fluences above the ablation threshold of F th≈60 J cm−2 (I th≈9 GW cm−2). Completely different excisions are produced by the femtosecond-pulse laser: high quality ablations of the Bowman membrane and the stroma tissue characterised by damage zones of less than 0.5 μm were observed at all fluences above ablation threshold of F th≈1 J cm−2 or I th≈3 TW cm−2 (3×1012 W cm−2). The transparent cornea material can be forced to absorb ultrashort pulses of extremely high intensity. The fs laser generates its own absorption by a multiphoton absorption process.